Environmental Protection Agency Administrator Lisa Jackson listens during a news conference at the National Press Club in Washington on Oct. 21, 2010. / Alex Brandon, AP

by Wendy Koch, USA TODAY

by Wendy Koch, USA TODAY

Environmental Protection Agency chief Lisa Jackson announced Thursday that she's stepping down after a four-year tenure marked by her agency's first greenhouse gas regulations and repeated battles with industry groups and GOP lawmakers.

Jackson, the first African American to serve as EPA administrator, came into office with bold plans to address climate change but accomplished only part of her agenda, foiled by opposition on Capitol Hill and occasionally the White House.

She often faced harsh congressional grilling. Last year, the GOP chairman of the House Energy and Commerce Committee, Michigan Rep. Fred Upton, said she would need her own parking spot at the Capitol because he planned to summon her often for questioning.

Jackson, 50, a chemical engineer by training and a mom of two teenagers, offered no reason for her resignation other than saying she's ready for "new challenges, time with my family and new opportunities to make a difference." She said she was leaving the EPA "confident the ship is sailing in the right direction."

Her departure, slated to occur after President Obama's annual State of the Union address in January, comes amid other turnover that's common between presidential terms. Secretary of State Hillary Rodham Clinton is leaving as is Jane Lubchenco, the head of the National Oceanic and Atmospheric Administration. Others, including Energy Secretary Steven Chu, are likely to follow.

"It's unusual for administrators to stay for more than one term. These jobs are grueling, non-stop," said David Goldston, director of government affairs for the Natural Resources Defense Council, an environmental group.

"She's been an outspoken fighter for environmental protection," Goldston said, noting the EPA's signature finding that carbon dioxide and five other gases that contribute to climate change qualify as pollutants under the Clean Air Act.

That "endangerment finding," which has withstood the industry's court challenges, enabled the EPA to set new emission standards for cars and light trucks. The standard requires new models to nearly double their required miles per gallon by 2025. In March, the EPA proposed emissions limits for new power plants, making it nearly impossible to build coal-fired ones.

Under her tenure, the EPA set the first standards for emitting mercury, arsenic and other toxins from power plants, and this month, it finalized tougher limits for emitting fine-particle soot from smokestacks, wood-burning stoves and diesel vehicles.

These rules won plaudits from environmentalists but rarely from industry. Howard Feldman of the American Petroleum Institute, which represents the oil industry, said the soot standard could increase energy prices and decrease jobs. "We fear this new rule may be just the beginning of a 'regulatory cliff,'" he said.

House Republicans, including Rep. Darrell Issa, R-Calif, have tried to thwart or delay EPA rules, alleging they'll increase unemployment, but the Senate has not gone along.

Citing such rules, President Obama praised Jackson in a statement Thursday, saying she has shown "an unwavering commitment to the health of our families and our children."

Jackson also had setbacks. She pushed for a cap-and-trade bill to cap greenhouse gas emissions but allow companies to buy pollution credits from those under the limits. The bill passed the Democratic-led House in 2009 but died in the Senate. Her agency's limits on industrial pollution crossing state lines were struck down by a federal court.

The White House delayed or weakened some of her other proposals, including a new standard for ozone pollution that she sought in summer 2011 but that Obama put off until his second term. The EPA's final standard on emissions from industrial boilers and cement factories, announced last Friday, was weaker than the proposed version.

Her efforts riled industry. "The onslaught of regulations from the EPA means manufacturers will continue to see rising energy prices and skyrocketing compliance costs, which translate into few opportunities for growth and even fewer jobs," Jay Timmons, president of the National Association of Manufacturers, said in a statement last week..

This month, at the prodding of congressional Republicans, the EPA's inspector general said he was opening an inquiry into Jackson's use of a secondary e-mail account for official business.She said she had the account - named "Richard Windsor" after the name of her dog and her former home in Windsor Township, N.J. - because her public e-mail address was well known.

Jackson, a native of New Orleans who spent much of her career as a staffer at the EPA before heading New Jersey's Department of Environmental Protection from 2006 to 2008, earned engineering degrees from Tulane and Princeton Universities. TheNew York Times and The Washington Post report she may be a candidate for president of Princeton.